Conventional combination squares include a polygonal housing for releasably frictionally retaining a typically graduated stainless steel 12″ grooved rule-type blade in a blade retaining slot for subtending a 90° shoulder and/or a 45° shoulder with opposite side surfaces of the housing. Exemplary combination squares with a screw operated L-shaped stopping member for engaging a grooved blade are disclosed in inter alia U.S. Pat. No. 3,824,700, U.S. Pat. No. 4,599,806, U.S. Pat. No. 5,174,446, U.S. Pat. No. 5,276,973, and U.S. Pat. No. 5,778,547. Commonly assigned U.S. Pat. No. 6,553,677 illustrates and describes a combination square with a pair of opposing housings having a manually operated clamping arrangement for engaging a grooved blade.
Use of a combination square involves frequent lengthwise adjustment of a blade along its blade retaining slot to newly desired positions. Each lengthwise adjustment requires an inconvenient releasing of a blade within a blade retaining slot and re-securing therein. Use of a combination square also involves less frequent but more time consuming and cumbersome accurate alignment and sliding re-insertion of a blade into its blade retaining slot to use different scales in the case that a blade is provided with same along opposite long edges or after using its housing as a spirit level in the case that it is provided with a bubble vial.